Thread: Desmog
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Old 12-13-2010, 03:51 PM
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RicardoJM RicardoJM is offline
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Join Date: Jul 2007
Location: Centennial, CO
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Originally Posted by subzali View Post
I know I have ported vacuum, I'm just not exactly sure where it is. I think ported vacuum means it's located above the throttle plates, so it only sees vacuum when the accelerator is pressed and the throttle plates are opened.
Your first sentence made me giggle. If you have the port just to the right of your idle mixture screw - it is very likely ported vacuum. That is to say, while the carbs have changed year to year a port in that location is where I have always seen it.

Originally Posted by subzali View Post
My big problem with taking the system back to stock is with my ignition/dizzy/carb. The PO said that the vehicle backfired with the smog pump hooked up (I never experienced that but didn't have the smog pump on for very long), and I wonder if that's partly a function of the '78 ignition, dizzy, and carb?
Yeah, because the systems and components vary year to year the one solid answer is to first determine where you want to be; desmogged, 77 year emissions or 78 year emissions - then you compile what is needed to get where you want to be. Easy to say (I know) and aside from dollars and sourcing parts; easy to do. Mix and match (what you have now) works, after all your truck is running proof.

Originally Posted by subzali View Post
...Ricardo, doesn't the big cap dizzy have multiple vacuum cans on it as well? Do you just have one plugged off?
Yes they do. I only use one. As I understand it; one of them is for vacuum advance and the other is for additional advance that is triggered by the high altitude compensation system. I do know that it is not advisable to run them both without the appropriate equipment managing them. I had Mr. Chenworth re-curve a big cap dizzy for my F.5 engine. I have not installed it yet, but it did come back from him with one of the "vacuum cans" capped off.
Ricardo Maestas - Bio Page
1999 LX 470
SOLD - 1971 FJ-40
TLCA #18941
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